Autometallographically enhanced Nanogold probes have proved highly sensitive both for direct detection of in situ hybridization probes, and when used in conjunction with Catalyzed Reporter Deposition (CARD, also known as Tyramide Signal Amplification or TSA). This method was used to detect Human Papilloma virus type 16 in SiHa cells known to contain only 1-2 copies of the viral genome more reliably than enzymatic detection. We propose a Nanogold chromogenic in situ assay for the detection of amplification of the proto-oncogene Her-2/neu in breast carcinoma specimens. This is the most widely accepted indicator of aggressive malignant behavior; the proposed assay will be used for early detection of potential malignancy and indication for monoclonal antibody or Herceptin therapy. Unlike fluorescent in situ hybridization (FISH) which requires fluorescent optics not routinely available in many pathology laboratories, Nanogold detection produces a dense black signal that is readily visualized by conventional optical microscopy. The new reagents and procedures will combine the high sensitivities of amplification with the ability of Nanogold to access restricted antigens, and the macromolecular spatial resolution which is only available with gold probes: the same sample may be processed for localization of the target sequence at the macromolecular level if desired. PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE